Indirect distributed garbage collection

Cronus [1-7] is an object oriented distributed system which operates in a heterogeneous computer environment of interconnected local area networks. As a distributed system architecture. Cronus faces a number of resource management issues not present in non-distributed architectures. Strategies for effectively controlling the redundancy and reconfigurability inherent in Cronus are needed to take advantage of the distributed system environment. These strategies for resource management are often conveniently separated into policies and mechanisms. A policy is a goal or guideline set by a system administrator or component designer constraining the decisions made by a resource allocator. A mechanism is an internal system structure designed to implement a class of policies.In the Cronus distributed system model, there are currently two general aspects of resource allocation mechanisms which are particular to the network environment and must be effectively managed. One of these is the binding of a client request to a particular resource manager for those resources which are available redundantly. Redundancy comes in two forms: replicated objects, (e.g., a multi-copy file) and replicated managers (any manager for a type can create a new instance of that object type). For both forms the selection of an object manager to provide the given service is an important resource management policy decision. The other important aspect of resource management mechanism is the ability to reconfigure parts of the system by dynamically migrating objects. Object migration is a powerful tool for matching system resources to tasks in a manner that attempts to maximize some measure of system performance, reliability, or survivability. Both static reconfiguration (e.g., choosing or amending the placement of object managers and their associated objects), and dynamic reconfiguration (e.g., moving an individual object in direct response to demand for its use possible in the Cronus architecture and design.The general approach to resource management in Cronus is to individually control the management of the classes of objects which make up the system. This approach extends Cronus resource management concepts beyond system resources to the abstract resources developed by applications. Resource management for an individual abstract resource (type) and for groups of related resource types (services) in Cronus is based on combining a number of carefully planned mechanisms which are part of the system architecture. In addition to resource management by resource type, a client specific policy which considers collections of object types used in a specific context can be constructed.In Cronus we achieve system wide and easily controllable resource management by requiring the object managers to cooperate in enforcing a resource management policy for their resource type. An object manager can redirect operations to a peer manager on another processor on the basis of current resource status. In the case for creation of a file to an alternate file manager which may have more storage available. Part of the basis for decisions to redirect requests are parameters, settable dynamically by system administrators through monitoring and control functions, which control the resource management strategy. The creation of objects and resource management in general thus becomes a responsibility that is decentralized among object managers on each processor based on a global allocation policy, both in terms of sharing current status and possible redirection of operations between managers.The Cronus resource management model is based on the integration of the following set of primitive mechanisms: the kernel routes requests for a given type to any available manager of that type, using the Locate mechanismCronus managers redirect requests to a more appropriate peer to accomplish resource management objectivesmanagers periodically collect current status of their peers, via a standard mechanism (ReportStatus), to be used as a basis for selecting a site for redirecting an operationusers and applications optionally indicate specific location preferences with requestsan operator can monitor and regulate the functioning of the resource management policyapplications can use the basic system mechanisms (e.g. broadcast or multicast, ReportStatus operations) to build special-purpose resource management strategies tailored to their needThere is a hierarchy of desirable locations for implementing resource management policies: object managers, shared libraries, and finally client programs or users themselves. Managers are the most desirable because they are readily identifiable with a limited set of object types which are likely to have similar policy goals. Also, managers are addressable as a group for administrative control to regulate the policy parameters, and for peer manager cooperation to implement the policy. Many decisions are negotiated between managers based upon information periodically obtained via the ReportStatus operation. The Cronus Monitoring and Control System uses the same ReportStatus operation to present the operator with a global view of how well the resource management policy is proceeding.In this paper we elaborate on these approaches to distributed resource management in Cronus, including appropriate background, detailed system design, and experiences with incorporating these ideas into three different resource managers.

The article describes the multi-object tracking system based on new approach to object management after preprocessing and background modeling. Object manager determine correlation between objects in previous and current frame by matching features. For matching features algorithm use color histogram with a small number of bins. Each moving object extracted from the scene is assigned to an individual and independent Kalman filter. System stores information about real position of the objects extracted directly from image processing and keep information about centroids predicted by Kalman filter.

This paper addresses the problem of garbage collection in persistent object stores that are multilevel. The proposed approach is able to preserve referential integrity, while ensuring that security is not violated. we first discuss some general principles that should underlie any approach to garbage collection in secure environments. Then, we present a secure garbage collection algorithm, based on the copying approach. >

HISC (High-level Instruction Set Computer) is proposed to provide hardware support for OOP. It applies the concept of object-orientation in the architecture and provides special instructions for object manipulation. An operating system is under developing for HISC. It divided into several modules by using the object-oriented paradigm. It includes some special modules for object-manipulation such as object management and garbage collection which traditional operating system do not support.In order to do the functional verification of each module, a test bench is needed. Its aims are to ease the effort to written the testing program and to simulate the working environment. It can make it easier to evaluate if an algorithm is suitable for HISC or not. In this paper, we discuss the design of the test bench. The architecture of the system will be described, together with the implementation of the modules and the pluggable modules architecture.

Basic study for realization of adaptation, evolution, and self-diagnosis on an artificial heart has been carried out by an autonomous distributed control system for an ultra-lightweight pulsatile VAD (volume of 285 ml and weight of 360 g). The autonomous distributed control system was build by 4 layers (input layer, measurement layer, control layer, output layer) and an object manager, which was realized on a l chip microcomputer (Hitachi, SH7044, Japan). The input and output layer are composed of ND, PIO, SIO for interface with the VAD. The measurement layer consists of 4 autonomous objects: current measurement, velocity measurement, position measurement, and timer. The control layer consists of 3 autonomous objects: position control, velocity control, and current control. The position and velocity control object are constructed by fuzzy inference algorism in order to build doctors' and engineers' knowledge into the VAD control. The object manager paces events on each object in order to maintain time series processes. The control system can he adapted to an axial flow VAD by exchanging the position measurement and position control object into a flow estimation and flow control object. In vitro experiment showed that The VAD was driven stably enough to maintain cardiac function by cooperation of independently operated each object like cells in the control system. In conclusion, the above results shows that the autonomous distributed control system promises suitability as a new superior artificial control system.

City of Huntington faces an issue of evenly distributed garbage collection among multiple fleets of trucks on different routes for fair amount of work for workers. This paper describes a method to estimate the weight of garbage picked by the trucks in each block of the city of Huntington based on a hypothesis of a correlation between the total number of stops and the total weight of garbage collected. A device was developed and mounted to the truck to collect data of truck movement. The data was analyzed to generate the number of stops the truck made and the results were compared with the weight of garbage collected throughout the route by a particular truck. Experimental results showed strong correlation between number of stops and garbage collected. Future enhancement is discussed.

We study tracing garbage collection (GC) for a distributed shared memory (DSM) in order to provide persistence by reachability (PBR), in a large-scale distributed system. Within a general model of DSM, we specify a distributed tracing GC algorithm that scales, collects cycles, and is orthogonal to coherence. Its main features are: (i) piecewise collection of opportunistically-chosen subsets of the memory, (ii) each site collects independently of other sites, (iii) data replicas are collected independently and no operation is needed for GC purposes; and (iv) asynchrony of collection with respect to applications.

In previous heap storage systems, the cost of creating objects and garbage collection is independent of the lifetime of the object. Since objects with short lifetimes account for a large portion of storage use, it is worth optimizing a garbage collector to reclaim storage for these objects more quickly. The garbage collector should spend proportionately less effort reclaiming objects with longer lifetimes. We present a garbage collection algorithm that (1) makes storage for short-lived objects cheaper than storage for long-lived objects, (2) that operates in real time—object creation and access times are bounded, (3) increases locality of reference, for better virtual memory performance, (4) works well with multiple processors and a large address space.

We have seen in the last chapter that in the area of distributed garbage collection algorithms exist, that detect whether one object is garbage depending on the number of references held by others. These other objects fit our definition of a dependency object in Definition 2-1 quite precisely, if we define a parent relation as “holds reference”. The problem of garbage collection is thus similar to the orphan detection problem for mobile agents. Moreover, the path created by local reference counters is similar to the paths in the path concept, i.e. in some algorithms we have an analogue to the problem how an agent can be found. Thus solutions that are similar to those proposed in Chapter 4 for the control of mobile agents have been developed in the area of distributed garbage collection.KeywordsMobile AgentTarget NodeLocal ReferenceGarbage CollectionParent ObjectThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Our everyday lives are becoming increasingly filled with mobile devices of varying capabilities. The common practice of creating multiple versions of the same application to cope with diverse device resource capabilities increases software development and maintenance costs. We discuss an offloading method to mask out the memory constraints on devices running a typical Java virtual machine. The method allows the garbage collector to selectively offload part of the object heap into a nearby wired server. In comparison with traditional virtual memory techniques, the garbage collector can make wiser offloading choices using information about object access patterns at a finer granularity. Our experiments show that our prototype introduces modest overhead in the JVM while allowing applications to execute on devices without enough physical memory. In addition, when running with the Linux virtual memory system under intense memory constraints, the prototype achieves an average improvement of 24% in run-time performance and 53% in energy savings.

In this chapter, we demonstrate the application of the various classes of thresholds, detailed in earlier chapters and elsewhere, via an actual but simplified natural resource management case study. We intend our example to provide the reader with the ability to recognize and apply the theoretical concepts of utility, ecological and decision thresholds to management problems through a formalized decision-analytic process. Our case study concerns the management of human recreational activities in Alaska’s Denali National Park, USA, and the possible impacts of such activities on nesting Golden Eagles, Aquila chrysaetos. Managers desire to allow visitors the greatest amount of access to park lands, provided that eagle nesting-site occupancy is maintained at a level determined to be acceptable by the managers themselves. As these two management objectives are potentially at odds, we treat minimum desired occupancy level as a utility threshold which, then, serves to guide the selection of annual management alternatives in the decision process. As human disturbance is not the only factor influencing eagle occupancy, we model nesting-site dynamics as a function of both disturbance and prey availability. We incorporate uncertainty in these dynamics by considering several hypotheses, including a hypothesis that site occupancy is affected only at a threshold level of prey abundance (i.e., an ecological threshold effect). By considering competing management objectives and accounting for two forms of thresholds in the decision process, we are able to determine the optimal number of annual nesting-site restrictions that will produce the greatest long-term benefits for both eagles and humans. Setting a utility threshold of 75 occupied sites, out of a total of 90 potential nesting sites, the optimization specified a decision threshold at approximately 80 occupied sites. At the point that current occupancy falls below 80 sites, the recommended decision is to begin restricting access to humans; above this level, it is recommended that all eagle territories be opened to human recreation. We evaluated the sensitivity of the decision threshold to uncertainty in system dynamics and to management objectives (i.e., to the utility threshold).

This research was conducted to evaluate the effectiveness and efficiency of the Simampu information system implementation at the Regional Disaster Management Agency (BPBD) of Serang Regency using the COBIT 5 framework. The information system was designed to assist BPBD in disaster data management, reporting, monitoring, and facilitating quick and accurate decision-making. However, the current implementation of Simampu was found to be suboptimal as it is still under development, and several issues were identified, such as system errors, network disruptions, and inadequate data security, hindering effective disaster data processing and reporting. The research utilized a qualitative approach involving direct observations and in-depth interviews with the system management team at BPBD Serang Regency. This study focused on four COBIT 5 domains: BAI01 (Manage Programmes and Projects), DSS02 (Manage Service Requests and Incidents), DSS03 (Manage Problems), and DSS05 (Manage Security Services). These domains were selected due to their relevance to BPBD’s operational needs and strategic objectives in disaster management. Findings revealed several weaknesses in the management of the Simampu information system, particularly concerning IT service management processes, incident handling, problem management, and information security services. To address these weaknesses, the researcher provided technical recommendations, including improvements in data security, network infrastructure enhancements, and optimization of data processing procedures.

It has been difficult to objectively assess the real value or maturity of the Object Management Group's Object Management Architecture (OMA). While experience reports have appeared in the literature, these have focused more on the functionality of the end-system than on systematically exploring the strengths and weaknesses of the OMA, and providing practical guidelines on the effective use of the OMA for specific software-engineering problems. In this paper we describe a case study in the use of the OMA to integrate legacy software components into a distributed object system. We assess the OMA in this problem context, and indicate strengths and weaknesses of the specification and current implementations. We extrapolate our experience to a broader class of component-based software systems, and recommend an architectural strategy for the effective use of the OMA to this class of systems.

A real-time garbage collector has to fulfill two conflicting properties: avoid heap fragmentation and provide short blocking time. The heap needs to be compacted to avoid probably unbounded fragmentation. During compaction all objects are copied; copying is usually performed atomically to avoid interference with mutator threads. Copying of large objects and especially large arrays introduces long blocking times that are unacceptable for real-time systems.In this paper an interruptible copy unit is presented that implements non-blocking object copy. The unit intercepts object and array field access and redirects the access either to the source or destination part of the moving object. The unit can be interrupted after a single word move. The resulting maximum blocking time is the time for a memory word read and write. We have implemented the proposed non-blocking copy unit in the Java processor JOP and are able to run high priority real-time tasks at 10 kHz parallel to the garbage collection task on a 100 MHz system.

Garbage collectors automatically free memory previously allocated by applications. Generally, they discard unreachable objects from memory, leaving reachable objects intact. However, object reachability does not necessarily imply usability, as an object may be obsolete and still reachable. Such objects are usually referred to as loitering objects. Loitering objects introduce a form of memory leak in a Java application. Predicting, tracing and eliminating loitering objects is a difficult problem. In this paper we address this problem. We present a self-healing approach for dealing with loitering objects. Specifically, the paper proposes an algorithm that can be integrated within the Java garbage collector. The algorithm prevents memory leaks resulting from loitering objects by "paging" suspected live objects to disk and reloading them if they are required. As a proof-of-concept, we have implemented and validated the algorithm for the Java Virtual Machine. This could be a first step towards genuine self-healing of memory management problems.